46,329 research outputs found
Controlled quantum teleportation and secure direct communication
We present a controlled quantum teleportation protocol. In the protocol,
quantum information of an unknown state of a 2-level particle is faithfully
transmitted from a sender (Alice) to a remote receiver (Bob) via an initially
shared triplet of entangled particles under the control of the supervisor
Charlie. The distributed entangled particles shared by Alice, Bob and Charlie
function as a quantum information channel for faithful transmission. We also
propose a controlled and secure direct communication scheme by means of this
teleportation. After insuring the security of the quantum channel, Alice
encodes the secret message directly on a sequence of particle states and
transmits them to Bob supervised by Charlie using this controlled quantum
teleportation. Bob can read out the encoded message directly by the measurement
on his qubit. In this scheme, the controlled quantum teleportation transmits
Alice's message without revealing any information to a potential eavesdropper.
Because there is not a transmission of the qubit carrying the secret message
between Alice and Bob in the public channel, it is completely secure for
controlled and direct secret communication if perfect quantum channel is used.
The feature of this scheme is that the communication between two sides depends
on the agreement of the third side.Comment: 4 page
One Dimensional ary Density Classification Using Two Cellular Automaton Rules
Suppose each site on a one-dimensional chain with periodic boundary condition
may take on any one of the states , can you find out the most
frequently occurring state using cellular automaton? Here, we prove that while
the above density classification task cannot be resolved by a single cellular
automaton, this task can be performed efficiently by applying two cellular
automaton rules in succession.Comment: Revtex, 4 pages, uses amsfont
On measuring the Tully-Fisher relation at
The evolution of the line width - luminosity relation for spiral galaxies,
the Tully-Fisher relation, strongly constrains galaxy formation and evolution
models. At this moment, the kinematics of z>1 spiral galaxies can only be
measured using rest frame optical emission lines associated with star
formation, such as Halpha and [OIII]5007/4959 and [OII]3727. This method has
intrinsic difficulties and uncertainties. Moreover, observations of these lines
are challenging for present day telescopes and techniques. Here, we present an
overview of the intrinsic and observational challenges and some ways way to
circumvent them. We illustrate our results with the HST/NICMOS grism sample
data of z ~ 1.5 starburst galaxies. The number of galaxies we can use in the
final Tully-Fisher analysis is only three. We find a ~2 mag offset from the
local rest frame B and R band Tully-Fisher relation for this sample. This
offset is partially explained by sample selection effects and sample specifics.
Uncertainties in inclination and extinction and the effects of star formation
on the luminosity can be accounted for. The largest remaining uncertainty is
the line width / rotation curve velocity measurement. We show that high
resolution, excellent seeing integral field spectroscopy will improve the
situation. However, we note that no flat rotation curves have been observed for
galaxies with z>1. This could be due to the described instrumental and
observational limitations, but it might also mean that galaxies at z>1 have not
reached the organised motions of the present day.Comment: 13 pages, 7 figures, A&A accepte
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
Achievable efficiencies for probabilistically cloning the states
We present an example of quantum computational tasks whose performance is
enhanced if we distribute quantum information using quantum cloning.
Furthermore we give achievable efficiencies for probabilistic cloning the
quantum states used in implemented tasks for which cloning provides some
enhancement in performance.Comment: 9 pages, 8 figure
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